By looking at the ROM code, available software and the hardware layout I can now document most specialty registers in the ST Book from Atari. I hope it is useful to you. Also available at GitHub.
The main ROM for the ST Book starts at $e0000 and ends at $e3ffff (256kb large). At $e40000 starts the ROM-Disk (also 256kb large), which is automatically activated as drive P.
YM Port A
| Bit | Description |
|---|---|
| 0 | Side Select (S0SEL) |
| 1 | Disk 0 Select (D0SEL) |
| 2 | Disk 1 Select (D1SEL) |
| 3 | MAX241 Pin 20 (TI3) – RS232 RTS (/MFPRTS) |
| 4 | MAX241 Pin 6 (TI2) – RS232 DTR (/MFPDTR) |
| 5 | Centronics Strobe (STROBE) |
| 6 | IDE Reset (IDERESET) |
| 7 | FDD Dense Selection (FDD_DENSE_SEL) |
Autovector Interrupt Level 7 /POWER FAIL (NMI)
MFP Input Pins
| Bit | Description | ||
|---|---|---|---|
| 7 | Power Alarms (Power Alarms) (POWER_ALARMS-) = (/SRCLOW | /RTC_ALARM | /POWERON) |
| 6 | MAX241 Pin 22 (RD4) – RS232 CD (/MFPRI) | ||
| 5 | XDISKINT | ||
| 4 | KTDK (VBL) (KTOK) | ||
| 3 | XBLTINT | ||
| 2 | MAX241 Pin 26 (RD3) – RS232 CTS (/MFPCTS) | ||
| 1 | MAX241 Pin 5 (RD2) – RS232 DCD (/MFPCD) | ||
| 0 | Centronics Busy (BUSY) |
$D0000 – Unknown $D0004 – Unknown
$FF820B
| Bit | Description |
|---|---|
| 0 | 0: enable combo -> shadow controller video transfer, 1: disable combo -> shadow controller video transfer |
$FF827E
| Bit | Description |
|---|---|
| 0 | 0: Shadow Chip OFF |
| 1 | 0: /SHIFTER_OFF output (Unused in STBook) |
| 2 | 0: POWER_OFF (Turns off main VCC when high) |
| 3 | 0: /22ON output (turns off LCD Bias when HIGH) |
| 4 | 0: REFRESH_MACHINE output (turns on refresh controller) |
| 5 | 0: RS–232_OFF output (turns off +/- 10 generator) |
| 6 | 0: (Unused in STBook) |
| 7 | 0: MTR_POWER_ON (turns on IDE drive motor supply) |
$FF9200 (Configuration/Signal register)
| Bit | Description |
|---|---|
| 0 | 0: Power Button pressed /(POWER_SWITCH) |
| 1 | 0: Top is closed /(TOP_CLOSED) |
| 2 | 0: RTC Alarm triggered /(RTC_ALARM) |
| 3 | 0: “Common Source” voltage level below 7.2V /(SOURCE_DEAD) – triggers an NMI |
| 4 | 0: “Common Source” voltage level below 8.8V /(SOURCE_LOW) |
| 5 | 0: External Modem (Pin 10 on J204) /(MODEM_WAKE) |
| 6 | Reserved (always 1) |
| 7 | 0: Triggered from the Expansion Port /(EXPANSION_WAKE) |
| 8 | Reserved |
| 9 | Reserved |
| 10 | Reserved |
| 11 | Reserved |
| 12 | Reserved |
| 13 | SELF TEST (?) |
| 14 | LOW SPEED FLOPPY |
| 15 | DMA AVAILABLE |
$FF9210 8-bit Common Power Voltage Level in 100mV steps
$FF9214 8-bit Reference Voltage Level in 100mV steps